Metal lubrication process



United States Patent 3,481,762 METAL LUBRICATION PROCESS Michael A.Streicher, Wilmington, Del., assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware No Drawing. FiledMar. 10, 1966, Ser. No. 533,225 Int. Cl. B44d 1/02, 1/14 U.S. Cl. 117-4913 Claims ABSTRACT OF THE DISCLOSURE Metals to be deformed, e.g., byextrusion, drawing, etc., are lubricated by depositing a water insolublemetal oxalate coating on the surface of the metal and/or on the surfaceof the workpiece which is to deform the metal, impregnating the oxalatecoating with a suspension of graphite in lubricating oil, and thendecomposing the resulting graphite and oil-impregnated oxalate coating.The oxalate coating preferably comprises manganous oxalate depositedfrom an aqueous solution of manganese and oxalate ions at aconcentration equivalent to more than 20 grams/liter manganous oxalate.

In primary working operations such as extrusion, drawing, rolling andforging, there is extensive deformation and working of the metalworkpiece being shaped. Because of the great pressures and extensivedeformation which occurs, there are stringent requirements forlubrication between the workpiece and the die or other shaping means inorder to reduce power requirements as well as surface scoring, marring,and rupture and seizing between the workpiece and shaping means. Thisinvention provides such a lubricant. Although the applications oftechniques described herein can be applied to metals generally, thisinvention is particularly adapted for use with metals of Groups IVB toVIIB and VIII of the Periodic Table of Elements, as shown on pages 58 to59 of Langes Handbook of Chemistry, 7th edition (1949) and especiallythe more refractory and difiicultly worked on metals, such as titaniumand zirconium for which, in connection with some metal workingoperations, the-re have been no adequate lubricants.

The metal working lubrication process of this invention comprises:

(a) depositing a water insoluble metal oxalate coating on at least oneworking surface, i.e., on the shaping means, surface of the workpiece incontact therewith, or both,

(b) impregnating the oxalate coating with a suspension of graphite inhydrocarbon lubricating oil, and' (c) heating the resulting impregnatedcoating at a temperature above 320 F. (160 C.) to decompose theoil-graphite-oxalate coating without rapid combustion.

The first step in the process of this invention comprises depositing awater insoluble oxalate coating on at least one of each pair of surfaceswhich are brought into contact during the metal working operation, forexample, the die, billet, or both, during extrusion. Although anyoxalate which will form a water insoluble coating, for example asdescribed hereinafter, can be employed, oxalates of metals of atomicnumbers 24 to 28 are particularly preferred. Of these, manganous andferrous oxalates are particularly preferred, manganous because it formsparticularly thick adherent oxalate coatings in accordance with theunique deposition process described herein and ferrous oxalate becauseof its low cost and ease of application by the procedures describedhereinafter.

The oxalate coatings can be applied by a number of different proceduresincluding in situ direct reaction of an acidic oxalic acid solution withthe surface of the workpiece, in situ redox reaction of the surface ofthe workpiece with dissolved metal salts to yield insoluble oxalates,and a preferred process of the invention described hereinaftercomprising immersion of the workpiece in a supersaturated manganousoxalate solution.

As just indicated, a preferred process of this invention comprisesimmersing the surface to be lubricated in a bath supersaturated withrespect to manganese oxalate containing manganous and oxalate ionspresent in an amount equivalent to at least 20 grams of manganousoxalate per liter. Although the manganous and oxalate ions may beproduced in the form of their soluble precursors, for example, alkalimetal and ammonium oxalates, manganous acetate, chloride, bromide, or acombination of one or more of the foregoing, preferably oxalate isprovided by oxalic acid, and manganese by manganous nitrate or acombination of soluble salts which yields both manganous and nitrateions, for example, potassium permanganate, oxalic acid and sodiumnitrate or nitric acid. In this preferred process of this invention, themajor part of the coating is formed by precipitation of manganousoxalate from a supersaturated solution and the deposition does notdepend on continued dissolution or in situ reaction of the metal surfacebeing lubricated. As a result, the process is not self-stifling andcoatings of unusual thickness can be formed, such thick coating beingdesirable with particularly high reduction ratios. One uniquecharacteristic of the solutions of the preferred manganous oxalateprocess is the fact that manganese and oxalate ions are present inquantities greatly in excess of the normal solubility of manganousoxalate. They are indeed unstable but even at the elevated temperatureof the coating operation the manganese oxalate continues to precipitateover a period of several hours. This slow precipitation yields uniform,adherent layer formed on the metal. These solutions contain manganeseand oxalate ions equivalent to manganese oxalate, MnC O in excess ofabout 20 gm./liter. Concentration considerably above 20 gm./liter up to200 gm./liter or even more, are used and represent a considerable degreeof supersaturation. It is preferred that nitrate ions are present toenhance the coating action. Typical manganous nitrateoxalic acid coatingbaths are illustrated hereinafter. On immersion in fresh solution ofmanganous oxalate, another similar layer can be deposited on top of thefirst. This is in contrast to other known oxalating baths in whichre-immersion in a fresh bath is substantially without effect. To preventa drop in temperature of the oxalating solution, it is convenient topreheat the billet in boiling water until it is close to the temperatureof the oxalating bath. The bath can be operated from room temperature toboiling, and preferably about from -212 F. (37.8-100" C.)

The action of these manganese coating baths is enhanced, at leastinitially by the addition thereto of an anionic wetting agent such asthe sodium salts of organic derivatives of sulfonic acids, e.g., sodiumalkyl aryl sulfonates such as sodium dodecylbenzenesulfonate, sodiumdecylbenzenesulfonate and sodium octylbenzenesulfonate. Those marketedunder the trade mark Alkanol WXN are preferred. Other anionic wettingagents are illustrated in 3 Detergents and Emulsifiers-Up to Date, 1963,John W. McCutcheon, Inc.

Another form of this novel bath can be prepared by using potassiumpermanganate as the source of manganese. Although oxalic acid andpotassium permanganate are known to react quantitatively the reaction isdelayed until a certain concentration of manganous ions have slowlydeveloped which catalyze the reaction. By mixing potassium permanganateand oxalic acid in concentrations giving the quivalent of over 20 gm./liter MnC O the reaction is delayed so that the metal to be coated canbe immersed and the solution heated to the 170-212" F. (76.7-100 C.)range before much reaction occurs. In a few minutes reaction does occurand manganous oxalate is precipitated in the solution. A large portionof it precipitates on the metal surface as an adherent coating.Presumably the reaction involved is The presence of nitrate, added asNaNO or other convenient salt, or as HNO improves the coating action.Presumably the mechanism of coating is the same as when Mn(NO is used;the KMnO merely serves as a cheaper source of manganese ions which arethen precipitated as MnC O Solid manganous compounds or concentratedaqueous solutions thereof can be added continuously during the coatingoperation to maintain the desired concentration i.e., keep the solutionin the unstable or supersaturated state with respect to the manganousoxalate.

A pre-coat of ferrous oxalate can be used to promote the growth andadhesion of the manganese oxalate on the metal surface. In the case ofcoating iron or steel, iron oxalate is also present in the coating eventhough the bath is initially iron free. Presumably the oxalic acid firstreacts with the iron to dissolve it whereupon ferrous oxalateprecipitates as a conversion coating on the surface.

The manganese oxalate coatings, which can also contain iron oxalate orother similar oxalates, are admirably suited to the subsequent treatmentwith graphite and oil for producing the novel lubricant of thisinvention.

Another process for the deposition of oxalate coatings involvesimmersing the piece to be lubricated in an aqueous solution of a solublemetal oxalate which by reaction with the surface being lubricated isreduced to a cognate insoluble oxalate. This process can be used eitheralone or in combination with the direct reaction of acidic solutions ofoxalic acid with the surface being lubricated. For example, when iron orlow alloy steels are exposed to oxalic acid, ferrous ions are formed atanodic sites which are electrochemically equivalent to the amount ofhydrogen evolved at cathodic sites on the surface. The ferrous ionsreact with oxalate ions to form insoluble ferrous oxalate, which thenprecipitates on the surface of the dissolving metal to form an adherentlayer of crystals. Formation of this coating gradually reduces thedissolution of the metal and, therefore, only relatively thin coatingscan be formed by this process. The rate of formation of this coating canbe increased by adding another source of ferrous ions to the solution inthe form of ferric oxalate, which is soluble in oxalic acid. The resultis that at cathodic sites not only hydrogen ions are reduced to hydrogenatoms but also soluble ferric ions to insoluble ferrous ions. In suchsolutions the rate of the coating process is increased by (1) having twosources of ferrous ions in the dissolution of iron and reduction offerric ions and (2) by increasing the rate of the cathodic reaction viareduction of ferric ions which, in turn, increases the rate of theanodic dissolution reaction. Another advantage of adding a ferric saltto oxalic acid solutions is that this addition makes it possible to formferrous oxalate coatings on non-ferrous metals. For example, to formiron oxalate coatings on titanium the metal is exposed to a solution ofoxalic acid, ferric .4 oxalate and a fluoride. The fluoride is added toincrease the rate of attack of oxalic acid on titanium. The dissolutionof titanium metal to titanium ions at anodic sites makes possible thereduction of ferric to insoluble, ferrous ions and consequentprecipitation of a coating of ferrous oxalate at cathodic sites on thesurface of the titanium. Preferably, in the deposition of ferrousoxalate coatings the concentration of iron and oxalate ions in solutionare equivalent to about 5 to 20% by Weight of ferric oxalate.

Other oxalate deposition procedures which can be used in accordance withthis invention are described, for example, in US Patent 2,273,234, asWell as in US. Patents 2,577,887; 2,669,532; 2,774,696; 2,800,421;2,813,816; 2,935,431; and 2,987,427, which are incorporated herein byreference.

With the variety of metal oxalates available and the numerous metalsurfaces to be lubricated, it is not surprising that considerablyvariation occurs in the degree and quality of the coating obtained. Someof the oxalating solutions used will coat some of the metals far betterthan others. However, since either the workpiece or the tool surface canbe coated, there is always an operable combination available. Inaddition there are two ancillary steps which can be taken to enhance theoxalate coating step. These include, in addition to normal cleaning andpickling procedures, electroplating with another metal which oxalatesbetter, preseating the metal, activating by etching in a mixture ofsulfuric, hydrochloric and hydrofluoric acids, and abrading.

In many cases the use of a thin plating of iron or other readilyoxalated metal will provide a thicker oxalate coating. Metals such astitanium, columbium, and zirconium, which either do not react rapidlywith oxalating solutions, and which do not form insoluble oxalates, canbe iron plated to provide a substrate which will acquire a heavy oxalatecoating. Plating is especially useful when using the preferred manganesenitrate-oxalic acid solution. Any method of producing a thin adherentiron deposit can be used. However, electrodeposition has been found verysatisfactory. The deposit usually ranges from 1 mil to 10 mils (0.0254to 0.254 cm.) in thickness. Thicker layers can be used, but since theirsubsequent removal by pickling is usually contemplated the thinnerplates are preferred. The preferred method for preparing the surface forplating is sand blasting. The iron plate can be used advantageously on awork piece made by compaction of metal powders. In plating a workpieceor die with iron any electrolysis procedure which gives a reasonablyuniform deposit can be used. A good bath is a simple 15% solution ofFeSO in water. The preferred solutions are those adjusted to a pHranging from 1.6 to 2.6 in which the iron content may vary quite widely.The plating is carried out above 160 F. (71.1 C.), and preferablybetween 200 F. (93.3 C.) and boiling to assure a ductile, adherentdeposit. At pH values below 1.6 and a current density of 10 arnps./dm.the current efficiency is low due to re-solution of the iron which canlead to discontinuities in the plate. At pH value above 2.6, the depositis non-uniform due to tree formation. A current density range of from 5to 20 amperes per square decimeter has been found satisfactory.

It has also been discovered that the process of coating metals withoxalate by immersion in any oxalating bath is improved by preheating themetal to temperatures up to about 212 F. C.), and preferably 100 to 212F. (37.8 to 100 C.). The improvement lies chiefly in obtaining a thickercoating. To illustrate this the following two solutions were used incoating a low carbon steel.

(a) 850 ml. water, 99 g. oxalic acid, 99 g. ferric oxalate. (b) 900 ml.water, 45 g. oxalic acid, 118.6 g. 50% soln.

of Mn(NO Both solutions were used at 210 F. (99 C.) with immersion for30 min. In one case the .02 cm. thick steel was not preheated, in theother it was preheated in plain water to 210 F. (99 C.) with thefollowing results.

Wt. of coating This effect is present with other metals and metalliccompositions.

Metal surfaces can be activated toward these oxalating baths especiallythose containing manganese oxalate by roughening the surface with anabrasive of 80 to 120 grit size. This treatment is especially effectiveon nickel and the stainless steels. This action is not though to bemerely one of cleaning the metal surface since the grit size is quitecritical. Rather it is believed that the degree of roughness produced issuch that effective nucleation sites for initiating growth of theoxalate crystals are produced.

In other instances nickel or nickel alloys may be treated with a mixtureof sulfuric, hydrochloric, and hydrofluoric acids to activate thesurface for coating formation in the oxalic acid-maganese nitratesolution in which these alloys dissolve with difiiculty. This picklingtreatment enhances the deposition of adherent crystalline oxalatecoatings by forming a very thin seed bed of insoluble nickel oxalate forthe subsequent deposition of manganese oxalate.

The amount of oxalate coating varies depending on whether one or bothworking surfaces are lubricated and the extent of deformation in themetal working operation. In general, it is greater if only one surfaceis lubricated and increases with the reduction ratio. Usually, theoxalate coatings vary from 0.01 to 4 g./dm. and preferably .1 to 3g./dm. After the adherent oxalate coatings have been formed, they areusually rinsed in water and allowed to dry. Drying can be accelerated byheating in an oven, preferably below 100 C.

Having deposited an adherent oxalate coating on the surface of the metalto be lubricated, the next step in the process of this inventioncomprises impregnating the oxalate coating with a dispersion of graphitein a hydrocarbon lubricating oil, for example, by dipping theoxalate-coated metal in the suspension or by brushing, spraying orotherwise applying the suspension to the oxalate coating. Although theamount of suspension applied can vary widely, in general sufficient isinfused into the oxalate coating to yield 5 to 200% of graphite based onthe weight of oxalate coating. The graphite-oil suspension, which,depending on the particular materials employed, can vary from a fluidsuspension to a paste or grease-like composition, usually contains 5 to50%, and preferably 5 to 25% by weight of graphite based on the totalcomposition. The graphite, which can be natural or synthetic, ispreferably of colloidal size. Graphites having a number average particlesize of less than microns and especially less than 1 micron areparticularly preferred. The oil preferably has a flash point above 300F. (149 C.), and preferably is an asphaltic-base hydrocarbon lubricatingoil. Examples of such oils include asphalt-base oils such as Texaco738-738M as well as the various motor oils, transmission oils and heavyoils and greases meeting the foregoing criteria. Graphite in oildispersions such as those described in MILL-3572, Aug. 21, 1951, areparticularly convenient graphite-in-oil dispersions of the type usefulin this invention.

The final step of the basic process of this invention comprises heatingthe graphite-oil-oxalate combination at a temperature of at least 320 F.(160 C.) to initiate slow decomposition of the coating, i.e.,decomposition without rapid burning. The heat treatment is usuallycomplete when visual decomposition, i.e., smoking, stops. The heattreatment is preferably carried out at a temperature of from 400950 F.(204.4510 C.) for a period of about from 3 minutes to 3 hours. Althoughthe heat treatment can conveniently be carried out in air, particularlyif the lower temperatures are employed, in order to insure against rapiddecomposition particularly at higher heat-treatment temperatures, theheating can be done in inert or unreactive gases such as argon,nitrogen, carbon dioxide, or steam.

The heat treatment of the oxalate-oil-graphite coating is an essentialpart of the invention, and the marked improvement gained thereby obtainsonly when all constituents thereof are heated simultaneously. Duringthis treatment, the oxalates decompose to oxides. Usually there isevidence of charring of the oil and this contributes to the ultimatecomposition of the lubricating film by forming a pitch which binds thevarious solid phases and serves to maintain separation of the opposingworking surfaces and hold any additional oil or other lubricantsubsequently added. The solid phases which contribute to the lubricationare the graphite and the residual oxide decomposition products of themetal oxalates formed in the presence of decomposing oil. These oxidesare stable at the higher working temperatures and serve, inter alia, toseparate the working surfaces thus preventing seizing. In addition,oxides have been observed to exhibit plastic flow under the pressuresencountered in metal working operations. This action also contributes tothe lubrication. The amount of lubrication separately contributed byeither the graphite, the oil and its residues or the oxalate residues isquite minor compared to the effect of the combination and thissynergistic effect results only from the step of decomposing the oxalatein the presence of the oil and graphite.

The process of this invention can be used for improving any of theprimary metal working operations including extrusion, drawing, rolling,forging, etc., wherein extensive deformation and working of the metal isencountered. As previously indicated, either the shaping means and/orthe workpiece can be lubricated. The process of this invention findsparticular utility in extrusion especially of the more difliculty workedrefractory metals, such as titanium, columbium and zirconium for whichwear, seizing, extrusion pressure and surface finish problems hecomeacute with known methods for extrusion which are often solved only bycanning, i.e., enclosing object to be formed in a steel or coppercontainer followed by forming of the object, removal of the can andrefinishing.

The lubricant of this invention may be used over a wide range oftemperatures depending on the nature of the metal being worked and thedegree of reduction desired. Temperatures up to 2600 F. (1427 C.) havebeen successfully used. In most cases lower temperatures are desired formetallurgical reasons. Extrusions of titanium and drawing of steel riflebarrels at room temperature has been improved by this method.

The following examples describe specific applications of this inventionwithout implying any limitation thereof. Parts and percentages are byweight unless otherwise indicated.

EXAMPLE 1 Ductile titanium powder 30+200 mesh is hydrostaticallycompacted to of theoretical density and shaped to fit a tube extrusionpress having a liner of 2.15 inches (5.46- cm.) ID. and a chrome steel90 cone die contoured at the throat. The billet is axially drilled toreceive a 21/32-inch (1.67 cm.) mandrel mounted on the follower block.The die port is 1 -inch (3.18 cm.) diameter at the land. The workingsurfaces of the tools (die and mandrel) are cleaned, heated to C. in anoven, and immersed for 30 minutes at 98 C. in a solution containing 45g. oxalic acid, 75 ml. of a solution of 50% Mn(NO in water, and 1000 ml.of water (63 g./liter MnC O to yield an oxalate coating weighing 0.6 to0.7 g./dm. Tools are rinsed and air dried. The billet is oxalate coatedby preheating to about 100 C. and then immersing at 98 C. for 30 minutesin a solution containing 53 g. ferric oxalate, g. oxalic acid, 10 g. NaFand 1000 g. water, then rinsing and drying in air. Both the tools andthe billet are coated with graphite in oil and heated to decompose theoxalate and oil. The graphite particles have a number average particlesize of less than 1 micron, are substantially all less than 4 microns indiameter, and amount to 10% of the total of oil plus graphite. The oilis an asphalt base, lubricating oil having a flash point of 325 F.(162.8 C.), a pour point of F. (9.44 C.), and a viscosity of 110 to 135universal Saybolt seconds at 210 F. (99 C.). The weight ratio ofgraphite to oxalate after impregnation is about 0.5: 1. The tools areoven heated in heated in argon to 450 C. for about 5 minutes. The toolsare assembled in the press with the liner temperature at about 390 C.and given a final coat of the graphite dispersion. The billet is removedfrom the induction furnace dipped again quickly in the graphitepreparation and extruded at a ram speed of inches (50.8 cm.) per minute.The resulting extruded %-inch (1.9 cm.) tube of -inch (.16 cm.) wallthickness is about 4 ft. (122 cm.) long is smooth having a mirror-likesurface both inside and out, and is only slightly curved. The metal hastheoretical density except for the first 5 or 6 inches (12.7 or 15.2cm.) which sometimes are not worked as much as the rest. The tube iseasily straightened, annealed and is ductile enough to be furtherreduced by drawing. The dark bluish residue on the surface can beremoved easily with acid.

EXAMPLE 2 Ductile titanium powder 30+200 mesh is hydrostaticallycompacted to rough billets of approximately 95% of the theoreticaldensity. Three such compacts are machined to extrusion billets 2 inches(5 .08 cm.) in diameter with a 90 cone chamber on one end. An extrusionpress is fitted with a heated container, 2.05 inch (5.20 cm.) I.D.linerand a 90 cone die of steel. A mild steel follower block is used andthe press set for a ram speed of 16 in./min. (40.6 cm.). Prior to eachextrusion the die is cleaned, assembled in the press, heated to 375 C.and

- coated with a colloidal 10% dispersion of submicron graphite particlesdispersed in petroleum oil just before use. The oil is an asphalt baselubricating oil having a flash point of 325 F. (162.8 C.) and aviscosity at 210 F. (99 C.) of 110 to 135 universal Saybolt seconds.

The three machined billets are preheated to about 212 F. (100 C.) by 20minute immersion in boiling water. Each warm billet is then immersed for30 minutes at 98 C. in a solution containing 53 g. ferric oxalatehexahydrate, 10 g. oxalic acid dihydrate, 10 g. sodium fluoride and 1000g. water to form the oxalate coating having a weight of about 0.2 to 0.3g./dm. The billets are then air dried and cooled to room temperature.

Billet A.The coated billet is dipped in the graphite dispersion andextruded into a /2-inch (1.27 cm.) rod at room temperature. The surfaceof the extruded rod is rough and torn.

Billet B.-The coated billet is heated by induction in argon to 450 0.,held 5 minutes to decompose the oxalate, and cooled in argon to roomtemperature. The cooled billet is dipped in the graphite dispersion andextruded into a rod of the same dimensions as those of A. The extrudedsurface is rough and scored.

Billet C.The coated billet is first dipped in the graphite dispersion(oxalate graphite ratio 0.5 :1) and then put through the same oxalatedecomposition cycle as Billet B, cooled to room temperature and extrudedinto a rod of the same dimensions as those of A and B. The extrudedsurface is smooth and substantially free of evidence of galling andillustrates this invention by showing the marked advantage resultingfrom thermally decomposing the oxalate while in contact with thegraphite-in-oil lubricant. Furthermore, the improved lubrication isevident even under the extreme conditions encountered during roomtemperature extrusion of titanium.

EXAMPLE 3 A titanium powder billet 4 inches (10.2 cm.) long is compactedand shaped to fit a 2.15-inch (5.46 cm.) diameter liner and a cone die.The working surface of the die is coated by contacting it with anoxalating solution at 96 C. for 20 minutes. The solution contained 99 g.oxalic acid, 99 g. ferric oxalate and 850 g. water. The oxalate coatingon the die (2 g./dm. was dried, swabbed with a viscous 10% dispersion ofcolloidal graphite in a heavy petroleum oil (e.g., Grade C, MIL-3572,Aug. 21,

l951graphite/oxalate 0.5 :1), and heated to 350 C. in air for 10minutes. After covering the bare billet with colloidal graphite inpetroleum oil it is heated in argon to 450 C. The press is assembled,all working surfaces given a final graphite dispersion coating and thebillet extruded to a /2-inch (1.27 cm.) rod. The extruded surface issmooth.

Improved lubrication is also obtained if an equal weight of cericoxalate is substituted for ferric oxalatein the lubrication proceduredescribed above.

EXAMPLE 4 A cast 8-inch (20.4 cm.) long ingot of a columbiumbase alloycontaining 1% zirconium is machined to a billet 4 inches (10.2 cm.) indiameter and 8 inches (20.4 cm.) long having a 90 chamber at one end. A1.5-inch (3.80 cm.) diameter axial hole is drilled through it. Thebillet is iron plated, then oxalated as described in Example 2. Theworking surfaces of an extrusion press, having a steel cone die with a2-inch (5.08 cm.) round opening, and a 1.49-inch (3.78 cm.) diametermandrel mounted on a follower are coated by immersion for a half hour at98 C. in a solution containing 45 g. oxalic acid, 50 ml. of a 50%manganous nitrate solution and 1000 g. water. The coating is rinsed withwater and dried to yield a coating weighing 2 g./dm. A 10% viscousdispersion of graphite in a petroleum oil similar to that in Example 3is spread over the oxalte coating on both die and mandrel(graphite/oxalate .5 :1) which are then placed in an oven at 375 C. forone hour. The uncoated billet is heated to 585 C. in argon by induction.The press is assembled, the container heated to 475 C. and the toolsurfaces swabbed with a conventional commercial metal working lubricant.The heated billet is transferred quickly from the argon furnaceatmosphere to the press and extruded to a smooth surfaced tube 2 inches(5.08 cm.) in diameter and 5 feet (152 cm.) long having a wall Mz-inch(.635-cm.) wall thickness by use of a break through pressure of 132,000p.s.i. (9,300,000 g./ cm?) calculated on billet cross section.

EXAMPLE 5 A 10% thoria dispersion modified nickel billet is machined toa 2-inch (5.08 cm.) diameter billet, 4 inches (10.2 cm.) long with a 90cone end. The billet surface is etched by 5 minutes immersion at 90 C.in a solution containing 600 ml. of 50% H SO ml. of 37% HCl and 25 ml.of 48% HF, then quickly transferred without rinsing to a coating bath at98 C. containing 950 g. water, 45 g. oxalic acid and 40 g. of Mn(NO(about 63 g./liter MnC O for half an hour. The oxalate coated billet isrinsed and air dried, coated with a graphite-oil dispersion similar tothat of Example 1, and heated to 400 C. for about one hour in air(graphite/oxalate 0.5 :1). The die to be used is cleaned, polished,coated with the oil-graphite and heated to 350 C., then the press isassembled and the die and liner are swabbed with the dispersion. Thebillet is heated to 925 C. by induction and quickly transferred andextruded at a ram speed of 25 inches (63.5 cm.) per minute to a A-inch(1.9 cm.)

smooth rod about 30 inches long. A silimar extrusion using only thegraphite-oil suspension results in a scored extrusion and evidence ofdie wear.

EXAMPLE 6 The metal used in this experiment is nickel containing 2% offinely dispersed thoria. A rod billet of this metal 4-inch (10.2 cm.)diameter by 8 inches (20.4 cm.) long is prepared having a conical end tofit the die used. The billet is electroplated with iron in a FeSOsolution with the acidity adjusted to pH 3. Three grams of iron persquare decimeter were deposited. This plated billet is coated withmanganese oxalate by immersion at 100 C. for 15 minutes in an oxalatingbath similar to that of Example 5, rinsed, air dried and coated withoil-graphite suspension as described in that example. The extrusionpress is assembled and the /z-inch (1.27 cm.) steel rod die heated to200 C. and coated with the suspension. The billet is then heated inargon from room temperature to 1700 F. (927 C.) and extruded to a smooth/z-inch 1.27 cm.) rod. In a control test, in which no oxalate coating isused, but other conditions are the same, a smooth rod results but thebreakthrough pressure is considerably higher. Removal of the iron plateby hydrochloric acid leaves a smooth nickel rod with a finish muchcloser to a polish than is obtained when extrusions are made with thebillet enclosed in a steel can.

EXAMPLE 7 Nine rod billets 2 inches (5.08 cm.) in diameter and rangingfrom 1%a-inch (4.75 cm.) to 3 /2-inch (8.9 cm.) long are prepared fromvarious batches of columbium base alloy nominally containing 10% Ti, 6%Mo and W. The billets are machined with 60 conical front ends to fit 60tool steel cone dies. The billets are all electroplated in ferroussulfate solution to give them approximately a 3 g./dm. codating of iron.These billets are then coated with oxalate by immersion for 20 minutesin a solution containing 50 g./liter oxalic acid, and 40 g./liter Mn(NOat 180 F. (82 C.). This coating is found to be chiefly manganese oxalatewith some ferrous oxalate in it. The latter results from the action ofthe oxalic acid on the iron plate. The extrusion press is a high speeddevice known as a Dynapac. In this device the billet is forced throughthe die by a ram in the usual manner except that the ram is activated bythe sudden release of gas pressure. The plated and coated billets areprepared for extrusion into 1 inch rods by dipping them in a dispersionof graphite in lubricating oil, draining and heating in argon to varioustemperatures ranging from 2370 F. (1299 C.) to 2500 F. (1371 C.)(oxalate 2 g./drn. graphite/oxalate 0.5:1). The extrusion times varyfrom 0.008 to .015 seconds depending apparently on the composition. Theextrusion pressures range from 150,000 to 210,000 p.s.i. (10,500,000 to14,800,000 g./cm. on the billet cross section. Straight rods having goodsurfaces are produced. The best surfaces are obtained at the lowertemperatures. Clean separation of the butt from the die is obtained inall cases. In control tests using graphite-in-oil in conjunction withglass as a lubricant, the rod surfaces were rought, cracked, or pittedindicating seizure between die and extrusion. Furthermore, the dies hadto be discarded or recovered by machining out the butts.

EXAMPLE 8 Small samples of a chrome die steel about 5% Cr, 0.35% C,0.12% V, 0.5% M0, 0.9% Si, are degreased with acetone, rinsed withwater, dried, weighed and immersed for 30 minutes at about 98 C. incoating baths having the compositions shown in the following table. Atthe end of 30 minutes the test pieces are withdrawn, rinsed with waterand dried at room temperature. The coating weights in the table aredetermined by first weighing the coated specimens then subtracting theweight of Coating Tool Steel Composition, percent Wt. 01 Coating,

Mn(NO (00 OH) 1211 0 mgJdmJ The coatings obtained are uniform inthickness and not easily removed. The outer part can be scraped oif witha sharp probe but considerable efiYect is required to'scrape the metalbare. The crystalline coating is shown by X-ray to be manganous oxalate.The lubrication process of this invention is completed by impregnatingthe oxalate coatings with graphite-oil suspension and heating theresulting products as described in the preceding examples.

EXAMPLE 9 A series of oxalating solutions of somewhat differentcompositions are prepared and used to coat samples of the vPD3 steeLThecompositions and weight of coating formed are shown below. Coatingconditions were 30 min. at 98 C.

Composition, g./1.

Coating,

MI1C304 N3(NO )Q H 090 mgJdmfl The coatings are of substantially thesame character as those in Example 8. Some oxalate is precipitated inthe beaker. In this series the manganese is added to the solution asmanganese oxalate. Although the solubility of MnC O is slight, for somereason not clearly understood, enough initially dissolved in thepresence of the sodium nitrate and oxalic acid to provide for thedesired reprecipitation of it on the metal during the heating period.The coatings are oil-graphite impregnated and heated as described in thepreceding examples.

The thickness of coating can be increased in the more difiicult case bypreliminary treatment or cleaning of the surface by acid pickling ormechanical abrading as shown in the following example.

EXAMPLE 10 A coating bath is prepared by dissolving 76.5 ml. of a 50%solution of manganous nitrate and 40 g. of hydrated oxalic acid in 900ml. of water. This solution was heated to 210 F. (99 C.). The samples ofmetal are all degreased with acetone and some, as indicated in thefollowing table, are pretreated mechanically or chemically andimmediately immersed in the bath at temperature for 30 minutes. Freshsolutions are prepared as needed so that the bath is never more than onehour old at the end of the treatment.

Activating Weight Metal Pretreatment (g./sq. dm.)

None 2.6

.............. Mechanical 0.762

A181 446 (25% Cr)-.. Chemical 1. 46 A181 304 (18 Cr-8 Ni) do. 4. 42 AISI316 (CrNiMo). Mechanical 0. 776 A181 310 (25 Cr2oNi) "do? 1. 28Carpenter 20 (20 (Jr-29 Ni-2 Mo3 Cu) (10. 1. 52 Nickel None 0.731 DoMechanical 2. 37

Do Chemical 1.38 Do do.- 0. 962 Nickel2% Thoria Mechanical 0. 996Inconel (72 Ni-l7 C do. 0. 822 Nionel (80 Ni-20 Cr) do. 4. 20 Nichromedo. l. 54 Do Chemical 2.82 Hastelloy B (65 Ni-30 Mo) Mechanical 0. 965Hastclloy C (55 Ni-15 Cr-l Mo)- (10. l. 49 Hastelloy F (44 Ni-22 Cr-24Fe) 2. 12 Copper 2. 14 Brass (70 Cu-30 Zn) 2. 58 antalum "do! l. 42Columbium .do. 0. 471 Zirconium do. 0. 270

1 Abrading with 80grit emery paper. 1 Immersed in solution oi:

600 ml. 50% sulfuric acid. 100 ml. 37% hydrochloric acid. 25 ml. 48%hydrofluoric acid at 90 C. for 5 min.

3 Immersed in solution of 37% hydrochloric acid at 70 C. for 5 min. Ifheavier coatings are desired, some more easily coated metal such as ironis first placed on the diificult metal, e.g., titanium, and themanganese oxalate coating then applied. When iron is first plated on themetals above, except for the first two, the adhesion of the oxalatecoating is enhanced. The lubrication process of this invention iscompleted by impregnating the oxalate coatings with graphite-oilsuspension such as that used in Example 1 at a graphite-oil ratio of 0.5:1; then heating the resulting product to about 450 F. (232 C.) for 30minutes.

EXAMPLE 11 Water. 1, 100 g. 5% oxalic acid. Ml'l(N03)z 50% soln. 94 ml.ferric oxalate. Oxalic acid. 55 g. Water.

The barrels are immersed at 100 C. for 30 min., removed, rinsed and airdried. A 10% graphite dispersion in petroleum oil similar to that ofExample 1 is then poured through each barrel to coat the interior. Thebarrels are then heated to 800 F. for one hour. The blanks are thenclamped on the draw bench and the rifling plug of tungsten carbidepushed through at room temperature. The maximum pressures required toforce the plugs through are 72 and 82 p.s.i. (5060 and 5760 g./cm.respectively, for the iron oxalate and manganous oxalate coated blanksrespectively. In all cases the surface and condition of the rifiingmarks are satisfactory.

EXAMPLE 12 Two tube billets of Zircaloy are prepared from an ingot. Thebillets machined to 4-inch (10.2 cm.) diameter x 8-inch (20.4 cm.) longwith a l /z-inch (3.80 cm.) axial hole for insertion of the mandrel. Theend is made conical to fit the steel cone die used. Zircaloy contains1.45% Sn, 0.125% Fe, Cr, 0.05% Ni with the balance being zirconium. Bothbillets are electroplated with iron, 3 g./ sq. dm., over the entiresurface and coated with manganese oxalate at a coating weight of 2g./dm. by immersion for 30 minutes at 98-100 C. in a freshly preparedsolution containing 1000 g. water, 45 g. oxalic acid, 35 g. Mn(NO 0.25g. of Alkanol WXN which is an aralkyl sodium sulfonate wetting agent.The die and mandrel for the first billet are also similarly coated withmanganese oxalate. Both billets and the die and mandrel for the firstbillet are immersed 'in an oil-graphite suspension similar to that ofExample 1 (graphite/oxalate 0.5:1), drained and heated to 540 C. Thetools for the second billet are not oxalate coated. Just prior to eachextrusion all working surfaces were swabbed or dipped in oil-graphitesuspension containing some dispersed molybdenum disulfide. Afterextrusion at 540 C. the surfaces of the resulting tubes, five ft. (152cm.) long with A-inch (.635 cm.) thick walls, are mirror-like anduniform.

EXAMPLE 13 Hollow cylindrical extrusion billets of 55-A titanium(0.25-inch (.635 cm.) thick) on 1020 steel (0.85 inch (2.16 cm.) thick)are electroplated with iron to a weight of 3 g./sq. drn. on outsidesurfaces and the bore. The billets are then oxalated and coated as shownin Example 11, Solution A. The mandrels are heated to 440 F. (226.7 C.)and the die to 850 F. (454.4 C.). A 2-inch (5.08 cm.) long billet isextruded to a 40-inch (102 cm.) tube at 1700 F. (926.7 C.) at a ramspeed of 2 inch/ min. (5.08 cm.). Both interior and exterior surfacesare excellent.

Billets comprised of 55-A titanium on OFHC copper and nickel on OHFCcopper are extruded in the same manner with similar results.

I claim:

1. A process for lubricating a metal surface[s] comprising at least onemetal selected from Groups IVB to VIIB and VIII of the Periodic Table,which comprises:

(a) depositing on said surface about from 0.01 to 4 g./dm. of waterinsoluble metal oxalate coating wherein the metal is of atomic number 2Ato 28 inclusive;

(b) impregnating said coating with a suspension comprising about from 5to 25% colloidal graphite, based on the total weight of the suspension,and hydrocarbon lubricating oil having a flash point above 300 F. (149C.), the amount of graphite thus impregnated in said coating being about5 to 200% based on the weight of metal oxalate; and

(c) heating the resulting impregnated coating at a temperature above 320F. C.).

2. A process of claim 1 wherein said oxalate is ferrous oxalate.

3. A process of claim 1 wherein a manganous oxalate coating is depositedon said surface by immersing said surface in an aqueous solutioncontaining the equivalent of at least 20 grams per liter of manganousoxalate.

4. A process of claim 3 wherein prior to deposition said surface isabraded with an abrasive of '80-120 grit size.

5. A process of claim 1 wherein said impregnated coating is heated at atemperature of from about 400 to 950 F. (204.4 to 510 C.).

6. In the process of metal extrusion, the improvement which compriseslubricating at least one of the die and work piece by the process ofclaim 1.

7. A metal surface lubricated with a coating obtained by the process ofclaim 1.

8. A process for a coating metal with manganous oxalate which comprisesimmersing said metal in an aqueous solution consisting essentially ofmanganese, nitrate and oxalate ions, the manganese and oxalate ionsbeing at a concentration equivalent to more than 20 grams/liter ofmanganous oxalate.

9. A process of claim 8 wherein the metal is coated 13 with iron oxalatebefore it is coated with manganous oxalate.

10. A process of claim 8 wherein the metal is stainless steel, carbonsteel or die steel, and the temperature of the aqueous solution is aboutfrom 180 to 212 F.

11. A process of claim 10 wherein the metal is preheated to about from180 to 212 F. before immersion in the aqueous solution.

12. A process of claim 8 wherein said metal is a thin coating of iron ona substrate of columbium, nickel, titanium, zirconium or an alloy basedon one of these metals, the temperature of the aqueous solution is aboutfrom 180 to 212 F., and the metal is preheated to about from 180 to 212F. before immersion in said solution.

13. A process for lubricating a metal surface that is coated with atleast about 0.01 g./dm. of water insoluble metal oxalate wherein themetal is of atomic number 24 to 28 inclusive, said metal surfacecomprising at least one metal selected from Groups IVB to VIIB and VIIIof the Periodic Table, which comprises:

(A) impregnating the coating of metal oxalate with a suspensioncomprising about from 5 to 25% colloidal graphite, based on the totalweight of the suspension, and hydrocarbon lubricating oil havingReferences Cited UNITED STATES PATENTS 4/ 1912 Dempster 72--42 4/ 1941Eddison 1l7127 XR 4/1943 Lowit 117--49 XR 11/ 1957 Otto.

5/1958 Rausch et al. 1486.14

6/ 1961 Shaw.

FOREIGN PATENTS 2/1961 France.

DAVID KLEIN, Primary Examiner US. Cl. X.R.

